Women who are involved in transactional sex remain are at substantial risk for HIV infection. Due to a confluence of social and structural factors, transactional sex is relatively prevalent among women from socially and economically marginalized groups, such as women who are Black and/or Latina, transgender, unstably housed/homeless and/or those who use and/or inject drugs. The overarching goal of this research is to decrease new HIV infections among women who engage in transactional sex. Daily oral HIV pre-exposure prophylaxis (PrEP) is an innovative method of HIV prevention that women, themselves, can control and that has the potential to reduce the risk of HIV acquisition among this risk behavior group. The objective of this study is to develop and pilot test a theory-guided behavioral intervention (PrEP-UP) which uses mobile street- based outreach (e.g., directly providing health services to persons living on the street via a mobile unit) to promote PrEP uptake among women involved in transactional sex. This proposal aims to: 1) elicit knowledge, attitudes, and beliefs about PrEP as well as feedback about PrEP-UP's proposed design; 2) develop a mobile street-based outreach intervention (PrEP-UP) to promote PrEP uptake among women involved in transactional sex; and 3) pilot test PrEP-UP for preliminary efficacy and feasibility. We will collaborate with an established multiservice, community-based organization (CBO) in the Bronx, NY which provides medical and psychiatric care via mobile street-based outreach to neighborhoods characterized by a high prevalence of poverty and HIV. The study aims will be achieved by conducting individual semi-structured interviews with women who report recent transactional sex using the Information-Motivation-Behavior Skills Model of HIV preventive behavior as a theoretical framework to inform the potential components of PrEP-UP. Based on this formative research, we will develop an intervention guide for PrEP-UP as well as determine the optimal processes for delivering PrEP-UP's behavioral content as well as directly providing PrEP and PrEP-related services (e.g., monitoring for side effects and adherence support) within the CBO's existing mobile street-based outreach infrastructure. In a pilot randomized controlled trial, we will preliminarily test PrEP-UP over a 12-week period for efficacy and feasibility by comparing PrEP-UP versus providing a PrEP education pamphlet plus transportation to a scheduled CBO clinic appointment. We hypothesize that participants randomized to PrEP- UP will have a higher rate of PrEP initiation, greater PrEP knowledge, more positive attitudes towards PrEP, and greater PrEP-related self-efficacy, as well as fewer HIV risk behaviors. Following this study, we will use feasibility data to further modify the PrEP-UP intervention and, in a fully powered randomized controlled trial, we will examine its efficacy at promoting PrEP among women who engage in transactional sex.